The Public Health Service's health promotion and disease prevention initiative established a national objective to reduce the proportion of low birthweight births. To meet this objective, we need a better understanding of the preventive role of prenatal care, as one relevant part of health services delivery. This study will provide important information, of which there is a relative paucity to date, about the relative effectiveness of different components of care in preventing poor pregnancy outcomes, namely low birthweight, preterm birth, and small for gestational age birth. Firstly, a methodological study will be undertaken to verify or revise four components of care which we have identified in our preliminary study. A panel of national experts will be used to assign levels of intensity to each set of services belonging to a component, using a modified Delphi technique. In general higher levels of intensity will be associated with more complex or more costly services, which in some instances will only represent appropriate care for higher risk mothers. Secondly, a population based case-control study is proposed. Cases, 560 mothers of low birthweight infants, will be compared to a random sample of 1079 control mothers who give birth to average or above average birthweight infants born at term with respect to the prenatal care they received. Two additional, overlapping, case groups will be recruited, and similarly compared to the controls. They are 751 mothers of preterm infants, and 992 mothers of infants who were born small for gestational age. Mothers will be interviewed, in hospital, following delivery, and their medical records iwill be abstracted. Mothers giving birth to infants at home, in birthing centers, or in hospitals outside of the study county will be identified from birth certificate data and interviewed at home. Cases and controls will be compared with respect to medical/obstetrical, behavioral, social and nutritional components of prenatal care using multiple logistic regression techniques, while adjusting for maternal risk factors and the quantity of prenatal care received.